Cook Strait Cable Fixed

Thursday 30th April 2009

Transpower engineers have fixed the break in the national grid connection which had cut the national power market in two since Monday evening.

The failure caused dismay for Prime Minister John Key and Energy Minister Gerry Brownlee, and plunged South Island power prices as low as two cents per Megawatt hour because no power could get from south to north after an HVDC transformer failure at Benmore.

South Island hydro schemes were running at full throttle at the time, with very heavy rainfall, all hydro catchment lakes full, and some water being spilled because it was more than could be used. North Island prices remained at relatively normal levels, around $60 per MWh.

The Pole two failure exposed a grave weakness in national electricity infrastructure which would have caused brownouts or blackouts in the South Island had it occurred during a dry period, when North Island electricity is essential to power the South.

The outage was caused by a complex circuit fault located outside the transformer.

Transpower operated Pole one of the HVDC for 24 hours during this time at a capacity of 130-200 MW. Pole one was taken out of service in late 2007 but can be operated for limited periods when necessary.

“Pole one operated without fault, thanks to the extensive maintenance that it’s been subject to over the last six months,” said Transpower CEO Patrick Strange.

The inter-island High Voltage Direct Current (HVDC) link includes two pairs of converter stations (Pole one and Pole two), which convert the power from AC to DC at Benmore and back to AC at Haywards – or the reverse for the increasingly common southward flow.

The first pole, Pole one, was commissioned in 1965. Pole two, on which the outage occurred, was added to the system in 1991.

Businesswire.co.nz

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